Vertical-channel type junction SiC power FET and method of manufacturing same

ABSTRACT

In order to secure the performance of a SiC-based JFET having an impurity diffusion rate lower than silicon-based one, a gate depth is secured while precisely controlling a distance between gate regions, instead of forming gate regions by ion implantation into the side wall of a trench. This means that a channel region defined by a gate distance and a gate depth should have a high aspect ratio. Further, due to limitations of process, a gate region is formed within a source region. Formation of a highly doped PN junction between source and gate regions causes various problems such as inevitable increase in junction current. In addition, a markedly high energy ion implantation becomes necessary for the formation of a termination structure. In the invention, provided is a vertical channel type SiC power JFET having a floating gate region below and separated from a source region and between gate regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2013-110780 filed onMay 27, 2013 including the specification, drawings, and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present application relates to a junction type power FET (orsemiconductor device) and a method of manufacturing the same, forexample, those applicable to a junction type SiC power FET.

Japanese Unexamined Patent Application Publication (Translation of PCTapplication) No. 2002-520816 (Patent Document 1) or U.S. Pat. No.6,847,091 (Patent Document 2) corresponding thereto mainly relates to aplanar type vertical power MOSFET. They show, with regard to a planartype vertical power MOSFET, a device structure having, in a driftregion, floating regions of a conductivity type opposite to that of thedrift region in a dispersed form. According to these documents, thispower MOSFET is applicable to a junction FET or the like.

Japanese Patent Application Laid-Open No. 2003-31591 (Patent Document 3)or U.S. Patent Application Publication No. 2002-167011 (Patent Document4) corresponding thereto relates to a vertical non-planar type junctionFET. These documents disclose a vertical type junction FET having alateral channel and having, in a drift region, a source potential regionhaving a conductivity type opposite to that of the drift region.

WO 2000/014809 (Patent Document 5) or U.S. Patent ApplicationPublication No. 2005-6649 (Patent Document 6) corresponding theretorelates to a vertical planar type junction FET. These documents disclosea vertical planar type junction FET having a floating P type regionbelow a lateral channel thereof.

-   [Patent Document 1] Japanese Unexamined Patent Application    Publication (Translation of PCT application) No. 2002-520816-   [Patent Document 2] U.S. Pat. No. 6,847,091-   [Patent Document 3] Japanese Patent Application Laid-Open No.    2003-31591-   [Patent Document 4] U.S. Patent Application Publication No.    2002-167011-   [Patent Document 5] WO 2000/014809-   [Patent Document 6] U.S. Patent Application Publication No.    2005-6649

SUMMARY

In a SiC-based JFET (junction FET) having a markedly low impuritydiffusion rate compared with a silicon-based JFET or the like, a gateregion is generally formed by forming a trench in a gate formationregion and then conducting ion implantation into the side wall of thetrench. In order to secure the performance of the JFET, it is necessaryto secure a gate depth while controlling the distance between gateregions with high precision. This means that a channel region defined bya gate distance and a gate depth should have a high aspect ratio. Inaddition, due to limitations of a process, a gate region is formed in asource region so that a heavily-doped PN junction is formed between thesource region and the gate region. This may pose various problems suchas inevitable increase in junction current. Further, ion implantationwith markedly high energies (about 2 MeV) is necessary for the formationof a termination structure.

A method of forming a gate region by conducting ion implantation at highenergies is considered as one of the methods of forming a gate regionwithout forming a trench. In this case, a distance between gate regionscan be controlled only by photolithography providing high precision andin addition, a distance between a source region and a gate region can beincreased by mask layout. This method however requires high energyimplantation so that it does not come to a complete technicalresolution.

Means and the like for addressing the above-mentioned problems willhereinafter be described. The other problem and novel features will beapparent from the description herein and accompanying drawings.

The outline of the typical embodiment, among embodiments disclosedherein, will be described below briefly.

The outline of the embodiment of the present application resides in avertical channel type SiC power JEFT having a floating gate below asource region and between gate regions.

An advantage available by the typical embodiment, among embodimentsdisclosed herein, will be described below briefly.

According to the one embodiment of the present application, a channelregion having a high aspect ratio can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary plan view of an active cell region fordescribing one example (source-island type orthogonal latticearrangement cell structure) of a unit cell structure in avertical-channel type junction SiC power FET (vertical planar typestructure) according to one embodiment of the present application;

FIG. 2 is a schematic cross-sectional view of a unit cell correspondingto the A-A′ cross-section of FIG. 1 and regions around the unit cell;

FIG. 3 is an overall top view (including an upper-surface metalstructure) of a chip for describing an overall chip layout(source-island type orthogonal lattice arrangement cell structure) inthe vertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application;

FIG. 4 is an overall top view (showing an emphasized contact portionwhile removing the upper-surface metal structure) of the chipcorresponding to FIG. 3;

FIG. 5 is an overall top view (showing an emphasized impurity regionwhile removing the upper-surface metal structure) of the chipcorresponding to FIG. 3;

FIG. 6 is a device cross-sectional view corresponding to the B-Ccross-section of FIG. 3;

FIG. 7 is a device cross-sectional view, corresponding to FIG. 6, duringa manufacturing step (gate region introduction step) for describing oneexample of a manufacturing process corresponding to the overall chiplayout (source-island type orthogonal lattice arrangement cell basicstructure) in the vertical-channel type junction SiC power FET (verticalplanar type structure) according to the one embodiment of the presentapplication;

FIG. 8 is a device cross-sectional view, corresponding to FIG. 6, duringa manufacturing step (floating region introduction step) for describingthe one example of a manufacturing process corresponding to the overallchip layout (source-island type orthogonal lattice arrangement cellbasic structure) in the vertical-channel type junction SiC power FET(vertical planar type structure) according to the one embodiment of thepresent application;

FIG. 9 is a device cross-sectional view, corresponding to FIG. 6, duringa manufacturing step (junction termination region introduction step) fordescribing the one example of a manufacturing process corresponding tothe overall chip layout (source-island type orthogonal latticearrangement cell basic structure) in the vertical-channel type junctionSiC power FET (vertical planar type structure) according to the oneembodiment of the present application;

FIG. 10 is a device cross-sectional view, corresponding to FIG. 6,during a manufacturing step (source region introduction step) fordescribing the one example of a manufacturing process corresponding tothe overall chip layout (source-island type orthogonal latticearrangement cell basic structure) in the vertical-channel type junctionSiC power FET (vertical planar type structure) according to the oneembodiment of the present application;

FIG. 11 is a device cross-sectional view, corresponding to FIG. 6,during a manufacturing step (interlayer insulating film formation &processing step) for describing the one example of a manufacturingprocess corresponding to the overall chip layout (source-island typeorthogonal lattice arrangement cell basic structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to one embodiment of the present application;

FIG. 12 is a device cross-sectional view, corresponding to FIG. 6,during a manufacturing step (surface metal film formation & processingstep) for describing the one example of a manufacturing processcorresponding to the overall chip layout (source-island type orthogonallattice arrangement cell basic structure) in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application;

FIG. 13 is a device cross-sectional view, corresponding to FIG. 6,during a manufacturing step (final passivation film formation &processing step) for describing the one example of a manufacturingprocess corresponding to the overall chip layout (source-island typeorthogonal lattice arrangement cell basic structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application;

FIG. 14 is a device cross-sectional view, corresponding to FIG. 6,during a manufacturing step (back-surface metal film formation &processing step) for describing the one example of a manufacturingprocess corresponding to the overall chip layout (source-island typeorthogonal lattice arrangement cell basic structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application;

FIG. 15 is a schematic cross-sectional view of a unit cell and regionstherearound corresponding to FIG. 2 for describing Modification Example1 (deep floating gate type source-island system cell structure) relatingto the unit cell structure (source-island type cell structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application;

FIG. 16 is a schematic cross-sectional view of a unit cell correspondingto FIG. 2 and regions therearound for describing Modification Example 2(trapezoidal floating gate type source-island system cell structure)relating to the unit cell structure (source-island type cell structure)in the vertical-channel type junction SiC power FET (vertical planartype structure) according to the one embodiment of the presentapplication;

FIG. 17 is a schematic cross-sectional view of a unit cell correspondingto FIG. 2 and regions therearound for describing Modification Example 3(inverted T-shaped floating gate type source-island system cellstructure) relating to the unit cell structure (source-island type cellstructure) in the vertical-channel type junction SiC power FET (verticalplanar type structure) according to the one embodiment of the presentapplication;

FIG. 18 is a schematic cross-sectional view of a unit cell correspondingto FIG. 2 and regions therearound for describing Modification Example 4(two-stage epitaxy inverted T-shaped floating gate type source-islandsystem cell structure) relating to the unit cell structure(source-island type cell structure) in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application;

FIG. 19 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 3 for describing ModificationExample 1 (stripe type source-island system cell structure) relating tothe overall chip layout in the vertical-channel type junction SiC powerFET (vertical planar type structure) according to the one embodiment ofthe present application;

FIG. 20 is an overall top view (having an emphasized contact portionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 19;

FIG. 21 is an overall top view (having an emphasized impurity regionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 19;

FIG. 22 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 4 for describing ModificationExample 2 (oblique lattice type source-island system cell structure)relating to the overall chip layout in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application;

FIG. 23 is an overall top view (having an emphasized contact portionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 22;

FIG. 24 is an overall top view (having an emphasized impurity regionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 22;

FIG. 25 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 3 for describing ModificationExample 3 (square lattice type gate-island system cell structure)relating to the overall chip layout in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application;

FIG. 26 is an overall top view (having an emphasized contact portionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 25;

FIG. 27 is an overall top view (having an emphasized impurity regionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 25;

FIG. 28 is a device cross-sectional view corresponding to the B-Ccross-section of FIG. 25;

FIG. 29 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 3 for describing ModificationExample 4 (stripe type gate-island system cell structure) relating tothe overall chip layout in the vertical-channel type junction SiC powerFET (vertical planar type structure) according to the one embodiment ofthe present application;

FIG. 30 is an overall top view (having an emphasized contact portionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 29;

FIG. 31 is an overall top view (having an emphasized impurity regionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 29;

FIG. 32 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 3 for describing ModificationExample 5 (deformed oblique lattice type gate-island system cellstructure) relating to the overall chip layout in the vertical-channeltype junction SiC power FET (vertical planar type structure) accordingto the one embodiment of the present application;

FIG. 33 is an overall top view (having an emphasized contact portionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 32;

FIG. 34 is an overall top view (having an emphasized impurity regionwhile removing the upper surface metal structure) of a chipcorresponding to FIG. 32;

FIG. 35 is a fragmentary schematic cross-sectional view of a portioncorresponding to the unit cell of FIG. 2 for describing the outline ofthe vertical-channel type junction SiC power FET according to the oneembodiment of the present application; and

FIG. 36 is a circuit diagram of a normally off composite type transistorshowing one example of a using state of the vertical-channel typejunction SiC power FET according to the one embodiment of the presentapplication.

DETAILED DESCRIPTION

[Outline of Embodiment]

First, the outline of typical embodiments disclosed herein will bedescribed.

1. A vertical-channel type junction SiC power FET including:

(a) a SiC semiconductor substrate having a first main surface and asecond main surface;

(b) a drift region provided from a surface to an inside on the side ofthe first main surface of the SiC semiconductor substrate and having afirst conductivity type;

(c) a drain region provided in a surface region on the side of thesecond main surface of the SiC semiconductor substrate, more heavilydoped than the drift region, and having the first conductivity type;

(d) an active cell region extending from a surface to an inside of thedrift region; and

(e) a plurality of unit cell regions provided in the active cell region.

In the FET, each of the unit cell regions includes:

(e1) a source region provided in a surface region of the drift region,more heavily doped than the drift region, and having the firstconductivity type;

(e2) a floating region provided in the drift region so as to be belowand contiguous to the source region and having a second conductivitytype, that is, a conductivity type opposite to the first conductivitytype; and

(e3) gate regions provided in a surface region of the drift region so asto sandwich therewith the source region and the floating region at leastfrom both sides thereof and having the second conductivity type.

2. In the vertical-channel type junction SiC power FET as describedabove in 1, a device structure belongs to a planar type.

3. In the vertical-channel type junction SiC power FET as describedabove in 1 or 2, an operation mode is a normally-on type.

4. In the vertical-channel type junction SiC power FET as describedabove in any one of 1 to 3, the floating region is formed by ionimplantation.

5. In the vertical-channel type junction SiC power FET as describedabove in any one of 1 to 4, the gate regions are formed by ionimplantation.

6. In the vertical-channel type junction SiC power FET as describedabove in any one of 1 to 5, the floating region is within the width ofthe source region in a planar view.

7. In the vertical-channel type junction SiC power FET as describedabove in any one of 1 to 6, the gate regions are arranged in a stripeform in a planar view.

8. In the vertical-channel type junction SiC power FET as described in7, the gate regions are linked with each other at an end portion of theactive cell region in a planar view.

9. In the vertical-channel type junction SiC power FET as describedabove in any one of 1 to 6, the gate regions are arranged in a mesh formin a planar view.

10. In the vertical-channel type junction SiC power FET as describedabove in 4, the floating region is formed by multistage ionimplantation.

11. In the vertical-channel type junction SiC power FET as describedabove in any one of 1 to 10, the floating region extends, in a depthdirection thereof, at least from a region between the gate regions to alower end of the gate regions.

12. A method of manufacturing a vertical-channel type junction SiC powerFET, having the steps of:

(a) providing an SiC semiconductor wafer having a first main surface anda second main surface, a drift region extending from a surface to aninside of the SiC semiconductor wafer on the side of the first mainsurface and having a first conductivity type, and a drain regionprovided in a surface region on the side of the second main surface,more heavily doped than the drift region, and having the firstconductivity type; and

(b) introducing, from a surface to an inside of the drift region, anactive cell region having a plurality of unit cell regions. The step ofintroducing the active cell region is performed for each of the unitcell regions and includes the sub-steps of:

(b1) introducing, in a surface region of the drift region, a sourceregion more heavily doped than the drift region and having the firstconductivity type;

(b2) introducing a floating region having a second conductivity type,which is a conductivity type opposite to the first conductivity type, inthe drift region so as to be below and contiguous to the source region;and

(b3) introducing gate regions having the second conductivity type in asurface region of the drift region so as to sandwich therewith thesource region and the floating region at least from both sides thereof.

13. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in 12, the floating region is introduced byion implantation.

14. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in 13, the floating region is introduced bymultistage ion implantation.

15. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in any of 12 to 14, the gate regions areintroduced by ion implantation.

16. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in any one of 12 to 15, a device structurebelongs to a planar type.

17. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in any one of 12 to 16, the sub-step (b2)is performed after the sub-step (b3).

18. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in any one of 12 to 17, the sub-step (b2)is performed before the sub-step (b1).

19. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in any one of 12 to 18, the floating regionis within the width of the source region in a planar view.

20. In the method of manufacturing a vertical-channel type junction SiCpower FET as described above in any one of 12 to 19, the floating regionextends, in a depth direction, at least from a region between the gateregions to a lower end of the gate regions.

[Explanation of Description Manner, Basic Terms, and Usage in thePresent Application]

1. In the present application, a description in embodiments may be madeafter divided in a plurality of sections if necessary for convenience'ssake. These sections are not independent from each other, but they mayeach be a part of a single example or one of them may be a partialdetail of the other or a modification example of a part or whole of theother one unless otherwise specified. In principle, a description of aportion similar to that described before is not repeated. Moreover, whena reference is made to constituent components in the embodiments, theyare not essential unless otherwise specified, limited to the numbertheoretically, or apparent from the context that they are essential.

Further, the term “semiconductor chip”, “semiconductor device”, or“semiconductor integrated circuit device” as used herein means mainly asimple transistor (active element) or a device obtained by integratingsuch a simple device as a main component with a resistor, a capacitor, adiode, and the like on a semiconductor chip or the like (examples of thematerial of the semiconductor chip include single crystal SiC substrateand single crystal silicon substrate, and composite substrate thereofand in the present application, 4H—SiC is a main crystal polymorph ofSiC, but it is needless to say that another crystal polymorph may alsobe used).

In the present application, the term “electronic circuit device” means asemiconductor chip, a semiconductor device, a semiconductor integratedcircuit device, a resistor, a capacitor, a diode, or the like and aninterconnected system thereof.

Typical examples of the transistor include a junction FET (junctionfield effect transistor).

In these days, each of the source and gate metal electrodes of apower-type electronic circuit device, semiconductor device, orsemiconductor integrated circuit device usually tends to be made of asingle layer which is, for example, an aluminum-based (or refractorymetal-based such as tungsten-based) wiring layer M1 or two layers madeof aluminum-based (or refractory-metal-based such as tungsten-based)wiring layers M1 and M2. As such wiring layers, copper-based wiringlayers are sometimes used. The term “power-type device” usually means adevice capable of handling electricity of several watts or greater.

2. Similarly, even when such a term “X comprised of A” or the like isused in association with a material, a composition, or the like in thedescription of the embodiment or the like, it does not exclude amaterial, composition, or the like containing an element other than A asone of the main constituent components thereof unless otherwisespecified or apparent from the context that it excludes such a material,composition, or the like. For example, with regard to a component, theterm means “X containing A as a main component” or the like. It isneedless to say that even the term “silicon member”, “SiC (siliconcarbide) member”, or the like is not limited to pure silicon or SiC butembraces a multi-element semiconductor containing silicon or SiC as amain component and a member containing, in addition, another additiveand the like. Similarly, it is needless to say that the term “siliconoxide film”, “silicon oxide-based insulating film”, or the like meansnot only a relatively pure undoped silicon dioxide but also aninsulating film having silicon oxide as a main component thereof. Forexample, a silicon oxide-based insulating film doped with an impuritysuch as TEOS-based silicon oxide, PSG (phosphorus silicate glass), orBPSG (borophosphosilicate glass) is also a silicon oxide film.Additional examples of the silicon oxide film or silicon oxide-basedinsulating film include a thermal oxide film, a CVD oxide film, and afilm obtained by the method of application such as SOG (spin on glass)and nano-clustering silica (NSC). Further, low-k insulating films suchas FSG (fluorosilicate glass), SiOC (silicon oxycarbide), carbon-dopedsilicon oxide, and OSG (organosilicate glass) are also silicon oxidefilms or silicon oxide-based insulating films. Still further,silica-based Low-k insulating films (porous insulating films, in whichthe term “porous” embraces molecular porous) obtained by introducingvoids into the same member as mentioned above are silicon oxide films orsilicon oxide-based insulating films.

As silicon-based insulating films, not only silicon oxide-basedinsulating films but also silicon nitride-based insulating films areordinarily used in semiconductor fields. Examples of materials belongingto such films include SiN, SiCN, SiNH, and SiCNH. The term “siliconnitride” as used herein means both SiN and SiNH unless otherwisespecifically indicated that it is not. Similarly, the term “SiCN” meansboth SiCN and SiCNH unless otherwise specifically indicated that it doesnot.

3. Preferred examples of the shape, position, attribute, and the likewill be shown below, however, it is needless to say that the shape,position, attribute, and the like are not strictly limited to thesepreferred examples unless otherwise specifically indicated or apparentfrom the context that they are strictly limited.

4. Preferred examples of the shape, position, attribute, and the likewill be shown below, however, it is needless to say that the shape,position, attribute, and the like are not strictly limited to thesepreferred examples unless otherwise specifically indicated or apparentfrom the context that they are strictly limited. Therefore, for example,the term “square” embraces “substantially square”; the term “orthogonal”embraces “substantially orthogonal”, and the term “coincide with”embraces “substantially coincide with”. This also applies to the terms“parallel” and “right angle”. For example, a position away by about 10degrees from a complete parallel position belongs to the term“parallel”.

The term “overall region”, “whole region”, “entire region”, or the likeembraces “substantially overall region”, “substantially whole region”,“substantially entire region” or the like. For example, the term“overall region”, “whole region”, or “entire region” embraces a portionof the region accounting for 80% or more of the area thereof. This alsoapplies to “whole circumference”, “whole length”, or the like.

Further, with regard to the shape of a member or the like, the term“rectangular” embraces “substantially rectangular”. For example, when amember has a rectangular portion and an unrectangular portion and anarea of the latter portion is less than about 20% of the whole area,this member is regarded rectangular. This also applies to the term“cyclic” or the like. In this case, when a cyclic body is divided, aportion having this divided element portion inserted therein or exsertedtherefrom is a part of the cyclic body.

With regard to the term “periodic”, the term “periodic” embraces“substantially periodic”. When a difference in periodicity amongcomponents is less than about 20%, these components are regarded“periodic”. Further, when less than about 20% of the components to beanalyzed are outside the above range, these components are regarded“periodic” as a whole.

The definition in this section is a general one. When a differentdefinition is applied to the following individual descriptions, priorityis given to the definition used in the individual description. Withregard to a portion not specified in the individual description, thedefinition or specification in this section is effective unlessotherwise definitely denied.

5. The term “wafer” typically means a single-crystal silicon carbidewafer, a single-crystal silicon wafer, or the like on which asemiconductor integrated circuit device (the same as a semiconductordevice or an electronic device) is formed. It is needless to say that italso embraces a composite wafer of an insulating substrate and asemiconductor layer or the like, such as an epitaxial wafer or an LCDglass substrate.

6. In the present application, a description will be made mainly on,among junction FETs, a vertical type junction (vertical junction) FEThaving a basic structure having a source electrode on the surface sideand a drain electrode on the back surface side. As another example ofthe junction FET, a lateral type junction (lateral junction) FET havingboth a source electrode and a drain electrode on the surface side can begiven.

The vertical type junction FET is classified into a lateral channel typehaving a main channel in a lateral direction and a vertical channel typehaving a main channel in a vertical direction. In the presentapplication, mainly a vertical channel type junction FET will bedescribed.

A specific description of a crystal plane (for example, the main surfaceof a SiC wafer) on which a device is to be formed will be made with a(0001) plane or a plane equivalent thereto as an example. A planeinclined by an angle within 10 degrees from the above-mentioned planesis also embraced in the plane equivalent thereto. It is needless to saythat if necessary, a device may be formed on another crystal plane.

[Details of Embodiment]

Embodiments will next be described more specifically. In all thedrawings, the same or like members will be identified by the same orlike symbols or reference numerals and overlapping descriptions will beomitted in principle.

In the accompanying drawings, hatching or the like is sometimes omittedeven from the cross-section when it makes the drawing cumbersome andcomplicated or when a member can be discriminated clearly from a vacantspace. In relation thereto, even a two-dimensionally closed hole mayhave a background outline thereof omitted when it is obvious from thedescription or the like that the hole is two-dimensionally closed. Onthe other hand, even a portion other than a cross section may be hatchedto clearly show that the hatched portion is not a vacant space.

With regard to alternative naming, when one of the two is called “first”and the other is called “second”, they are sometimes named according tothe typical embodiment, but needless to say, their naming is not limitedto this choice.

1. Example of Unit Cell Structure (Source-island Orthogonal LatticeArrangement Cell Structure) of Vertical-channel Type Junction SiC PowerFET (Vertical Planar Type Structure) According to One Embodiment ofPresent Application (Mainly FIG. 1 and FIG. 2)

This section describes the outline of a basic example to be described inSection 2 while referring to a schematically cutaway portion of a unitcell region and an active cell region which clearly show thecharacteristics of the example.

FIG. 1 is a fragmentary plan view of an active cell region fordescribing one example (source-island type orthogonal latticearrangement cell structure) of a unit cell structure in avertical-channel type junction SiC power FET (vertical planar typestructure) according to one embodiment of the present application. FIG.2 is a schematic cross-sectional view of a unit cell corresponding tothe A-A′ cross-section of FIG. 1 and regions around the unit cell. Basedon these drawings, one example of the unit cell structure (source-islandtype orthogonal lattice arrangement cell structure) in thevertical-channel type junction SiC power FET according to the oneembodiment of the present application will be described.

First, a schematic device structure from which the surface structuresuch as electrodes and insulating films on the surface and back surfacehas been omitted will be described. A schematic top view correspondingto an internal partially cutaway portion R1 of an active cell region 9of a semiconductor chip 2 of a vertical-channel type junction SiC powerFET is shown in FIG. 1. In this example, as shown in FIG. 1, thesemiconductor substrate 2 (for example, SiC substrate) in the activecell region 9 has, on a surface 1 a thereof, a number of unit cellregions 10 in an orthogonal lattice form. The orientation of thisorthogonal lattice corresponds to, for example, that of the lattice-formarrangement of chips on a wafer and a direction of sides of each of thechips adjacent to each other.

Each of the unit cell regions 10 is comprised of a P type gate region 4(normal gate region) at the periphery thereof, an N+ type source region6 formed inside of the gate region, a P type floating region 5 (floatinggate region) formed inside of the source region, and the like. The Ptype gate region 4 and the N+ type source region 6 are separated fromeach other by an N− type drift region 3 (for example, an N− type SiCepitaxy layer 1 e). In this layout, the P type gate region 4 is totallyin a mesh form in a planar view.

Next, the A-A′ cross-section of FIG. 1 is shown in FIG. 2. As shown inFIG. 2, the semiconductor substrate 2 has, in a surface region on theside of a back surface 1 b (second main surface) thereof, an N+ typedrain region 7 having a uniform thickness. On the other hand, thesemiconductor substrate 2 has, from the surface to the inside on theside of the surface 1 a (first main surface) thereof, an N− type driftregion 3 (for example, an N− type SiC epitaxy layer 1 e) having asubstantially uniform thickness. The N+ type drain region 7 has animpurity concentration greater than that of the N− type drift region 3.These regions each have an N conductivity type (for example, a firstconductivity type) so that they have the same conductivity type.

The N− type drift region 3 (drift region) has, in the surface regionthereof, the N+ type source region 6 (source region) having aconcentration greater than that of the N-type drift region 3. The N−type drift region 3 has therein the P type floating region 5 (floatingregion or floating gate region) below and in the vicinity of the N+ typesource region 6. The floating region 5 has a conductivity type (secondconductivity type) opposite to that of the N− type drift region 3.

The P type gate region 4 is provided from the surface to the inside ofthe N− type drift region 3 so as to sandwich the floating region 5 andthe source region 6 from at least both sides thereof. This gate regionmay be either a single region (in this example, for example, a singleregion in a mesh form) or an assembly of a plurality of regions.

Thus, the active cell region 9 is provided from the surface to theinside of the drift region 3 and the active cell region 9 has therein aplurality of unit cell regions 10. This device structurally belongs to aso-called planar type structure. With regard to an operation mode, it isa so-called normally on type. Needless to say, the operation mode of thedevice may be a so-called normally on type.

In this example, the N+ type source region 6, the P type floating region5, the P type gate region 4, and the like are formed by ionimplantation. In this example, for example, the P type floating region 5is formed by multistage ion implantation.

As is apparent from FIG. 2, in this example, the floating region 5 iswithin the width WS of the source region 6 in a planar view. The widthWS (for example, about 3 micrometers) of the source region 6 and thewidth WG (for example, about 1 micrometer) of the floating region 5 canbe given as a preferred example.

Similarly, the floating region 5 extends, in a depth direction, at leastfrom a region between the gate regions 4 to a lower end 4 b of the gateregion 4.

As shown in FIG. 2, the current path in a channel portion 23 (portionsubstantially limiting the flow of an electric current) is mainly in avertical direction so that this device structure belongs to avertical-channel type junction FET.

In addition to the main gate region 4, the P type floating region 5(auxiliary gate region) is provided as a floating region. It achievesshallow junction of the gate layer and as a result, has the advantagethat ion implantation at high energies becomes unnecessary.

Further, the auxiliary gate region 5 provided as a floating region hasthe advantage that a lead wiring becomes unnecessary.

Similarly, shallow junction of the gate layer has the advantage that ionimplantation in a junction termination region at high energies becomesunnecessary.

The distance of the main gate region 4 can be set at relatively wide sothat such a structure has the advantage that a distance with the sourceregion 6 can be made relatively wide.

Since in such a structure, the main gate region 4 has thereon no region,a metal gate wiring can be laid out right above the main gate region 4.Such a layout is effective for reducing gate resistance.

Moreover, this device is a vertical-channel type device so that anincrease in breakdown voltage can be achieved easily by increasing theaspect ratio of a channel region. On the other hand, an increase inbreakdown voltage of a lateral-channel type device is difficult becausean increase in the aspect ratio of a channel region leads to aproportional increase of a device size.

The device in this example operates in a normally on mode so that it hasthe advantage of excellent switching characteristics and relatively easymanufacture.

Alternatively, the device can operate in a normally off mode afteradjustment of the concentration or the like of each region.

Further, the device structure having a planar structure has theadvantage of manufacturing ease.

The auxiliary gate region 5 formed by ion implantation can omitadditional etching or epitaxy process because ion implantationfacilitates minute processing. This auxiliary gate region 5 is formed bymultistage ion implantation, which can increase the aspect ratio of thechannel region and thereby increase the breakdown voltage of the device.

Similarly, the main gate region 4 formed by ion implantation can omitadditional etching or epitaxy process because ion implantationfacilitates minute processing.

The auxiliary gate region 5 is within the width of the source region 6in a planar view. This facilitates downsizing of the device.

The auxiliary gate region 5 extends, in the depth direction thereof,from a region between the main gate regions 4 to the lower end (or thevicinity) thereof so that a sufficient channel length can be secured.

2. Description of an Overall Layout (Source-island Type OrthogonalLattice Arrangement Cell Structure) of a Chip in the Vertical-channelType Junction SiC Power FET (Vertical Planar Type Structure) Accordingto the Embodiment of the Present Application (Mainly, from FIG. 3 toFIG. 6)

In this section, the overall structure of the device corresponding tothe structure of the unit cell region 10 (FIG. 1, FIG. 2) describedabove in Section 1 will be described. In the following example, only aportion not described in Section 1 will be described in principle.

FIG. 3 is an overall top view (including an upper-surface metalstructure) of a chip for describing an overall chip layout(source-island type orthogonal lattice arrangement cell structure) inthe vertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application.FIG. 4 is an overall top view (showing an emphasized contact portionwhile removing the upper-surface metal structure) of the chipcorresponding to FIG. 3. FIG. 5 is an overall top view (showing anemphasized impurity region while removing the upper-surface metalstructure) of the chip corresponding to FIG. 3. FIG. 6 is a devicecross-sectional view corresponding to the B-C cross-section of FIG. 3.Based on these drawings, the overall layout (source-island typeorthogonal lattice arrangement cell structure) and the like of a chip ofthe vertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present applicationwill next be described.

The overall layout of the surface 1 a of the chip 2 is shown in FIGS. 3to 5. As shown in FIGS. 3 to 5, the chip 2 has, at the peripherythereof, the N− type drift region 3, that is, the N− type SiC epitaxylayer 1 e and the drift region has, inside thereof, a ring-shaped P typejunction termination region 8, that is, a junction termination extensionregion.

The p type junction termination region 8 has inside thereof, an outerperipheral portion of the P type gate region 4 (normal gate region) andthis gate region has, at the outer peripheral portion thereof, gatecontact portions 12 and a metal gate wiring 16 (metal gate electrode)that links them with each other. The P type gate region 4 further has,inside the outer peripheral portion thereof, for example, in the activecell region 9, the unit cell regions 10 arranged in an orthogonallattice form.

A substantially whole region of the active cell region 9 is covered witha metal source electrode 15 and this metal source electrode 15 iselectrically coupled to a source contact portion 11 of each of the unitcell regions 10. The metal source electrode 15 has, in an inside regionthereof, for example, a source pad opening 14 (opening portion of afinal passivation film).

Next, the B-C cross-section of FIG. 3 to FIG. 5 is shown in FIG. 6. Asis apparent from FIG. 6, the semiconductor substrate 2 has, in a surfaceregion on the side of the back surface 1 b (second main surface) of thesemiconductor substrate 2, the N+ type drain region 7 having, forexample, a uniform thickness. The semiconductor substrate 2 has, on theback surface 1 b thereof, a back-surface metal electrode film 19 (metaldrain electrode film).

On the other hand, the semiconductor substrate 2 has, from the surfaceto the inside thereof on the side of the surface 1 a (first mainsurface), has, in this example, the N-type drift region 3 (for example,N− type SiC epitaxy layer 1 e) having a substantially uniform thickness.

The N− type drift region 3 (drift region) has, in the surface regionthereof, the N+ type source region 6 (source region) more heavily dopedthan the N− type drift region 3. The N− type drift region 3 has thereinthe P type floating region 5 (floating region or floating gate region)so as to be below and at the same time, contiguous to this N+ typesource region.

The N− type drift region 3 has, from the surface to the inside thereof,the P type gate region 4 so as to sandwich therewith the floating region5 and the source region 6 at least from both sides of these regions.Further, the P type gate region 4 has, outside thereof, the p typejunction termination region 8.

The semiconductor substrate 2 has, on the surface 1 a thereof, forexample, an interlayer insulating film 17 such as silicon oxide film.This interlayer insulating film 17 has thereon the metal sourceelectrode 15 and is electrically coupled to the N+ type source region 6via the source contact portion 11. The interlayer insulating film 17 hasthereon the metal gate wiring 16 (metal gate electrode) and iselectrically coupled to the P type gate region 4 (normal gate region)via the gate contact portion 12. The interlayer insulating film 17, themetal source electrode 15, the metal gate wiring 16, and the like arecovered, except for a portion of them, with a final passivation film 18.

As described above, in the source-island type layout (the presentexample and the example of sub-sections (1) and (2) of Section 5), thesource region 6 and the auxiliary gate region 5 (P type floating region)are both in an island form, which provides the advantage that freedom ofthe layout of the main gate region 4 (P type gate region) becomes large.The auxiliary gate region 5, if it is not a floating region, hasdifficulty in leading of an electrode, but in the above example, thegate region is a floating region so that no problem occurs. In a planarview, the auxiliary gate region 5 is within the source region 6 (isincluded therein) so that areal effectiveness of such a structure ismarkedly high.

3. Description of One Example of a Manufacturing Process Correspondingto an Overall Layout (Source-island Type Orthogonal Lattice ArrangementCell Basic Structure) of the Chip in the Vertical-channel Type JunctionSiC Power FET (Vertical Planar Type Structure) According to theEmbodiment of the Present Application (Mainly, FIGS. 7 to 14)

In this section, one example of a manufacturing process corresponding tothe device structure described in Section 2 will be described. It ishowever a simple example and needless to say, it can be modified invarious ways.

A specific description will hereinafter be made with a device having asource-drain breakdown voltage of about 1000V as an example. Needless tosay, however, the breakdown voltage is not limited to it.

FIG. 7 is a device cross-sectional view, corresponding to FIG. 6, duringa manufacturing step (gate region introduction step) for describing oneexample of a manufacturing process corresponding to the overall chiplayout (source-island type orthogonal lattice arrangement cell basicstructure) in the vertical-channel type junction SiC power FET (verticalplanar type structure) according to the one embodiment of the presentapplication. FIG. 8 is a device cross-sectional view, corresponding toFIG. 6, during a manufacturing step (floating region introduction step)for describing the one example of a manufacturing process correspondingto the overall chip layout (source-island type orthogonal latticearrangement cell basic structure) in the vertical-channel type junctionSiC power FET (vertical planar type structure) according to the oneembodiment of the present application. FIG. 9 is a devicecross-sectional view, corresponding to FIG. 6, during a manufacturingstep (junction termination region introduction step) for describing theone example of a manufacturing process corresponding to the overall chiplayout (source-island type orthogonal lattice arrangement cell basicstructure) in the vertical-channel type junction SiC power FET (verticalplanar type structure) according to the one embodiment of the presentapplication. FIG. 10 is a device cross-sectional view, corresponding toFIG. 6, during a manufacturing step (source region introduction step)for describing the one example of a manufacturing process correspondingto the overall chip layout (source-island type orthogonal latticearrangement cell basic structure) in the vertical-channel type junctionSiC power FET (vertical planar type structure) according to the oneembodiment of the present application. FIG. 11 is a devicecross-sectional view, corresponding to FIG. 6, during a manufacturingstep (interlayer insulating film formation & processing step) fordescribing the one example of a manufacturing process corresponding tothe overall chip layout (source-island type orthogonal latticearrangement cell basic structure) in the vertical-channel type junctionSiC power FET (vertical planar type structure) according to oneembodiment of the present application. FIG. 12 is a devicecross-sectional view, corresponding to FIG. 6, during a manufacturingstep (surface metal film formation & processing step) for describing theone example of a manufacturing process corresponding to the overall chiplayout (source-island type orthogonal lattice arrangement cell basicstructure) in the vertical-channel type junction SiC power FET (verticalplanar type structure) according to the one embodiment of the presentapplication. FIG. 13 is a device cross-sectional view, corresponding toFIG. 6, during a manufacturing step (final passivation film formation &processing step) for describing the one example of a manufacturingprocess corresponding to the overall chip layout (source-island typeorthogonal lattice arrangement cell basic structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application.FIG. 14 is a device cross-sectional view, corresponding to FIG. 6,during a manufacturing step (back-surface metal film formation &processing step) for describing the one example of a manufacturingprocess corresponding to the overall chip layout (source-island typeorthogonal lattice arrangement cell basic structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to one embodiment of the present application. Basedon these drawings, the one example of a manufacturing processcorresponding to the overall chip layout (source-island type orthogonallattice arrangement cell basic structure) in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application will next be described.

First, as shown in FIG. 7, for example, an N type SiC semiconductorwafer (having, for example, a resistivity of about 20 mmΩcm) isprovided. This SiC wafer 1 (for example, 4H polytype) has a diameter of76φ (it may have a diameter of 100φ or 150φ , or another diameter) andthe crystal plane of the main surface is, for example, (0001) orequivalent thereto. The wafer has a thickness of, for example, about 350micrometer (the thickness falls within a range of from about 100 to 900micrometer as needed). A wafer having a main orientation flat and asub-orientation flat (these orientation flats are perpendicular to eachother) is used. With regard to the crystal orientation, for example, themain orientation flat has a [1-100] direction and a direction oppositeto the sub-orientation flat is, for example, a [11-20] direction. It isnot always necessary but in this example, each side of each of the chips(rectangle) is substantially parallel to either of the orientationflats.

The crystal plane of the main surface 1 a is not only, for example, a(0001) plane itself or plane equivalent thereto itself, but needless tosay, it may also be a (0001) plane similar to them in properties of thecrystal plane or a plane inclined by not greater than 10 degrees to apredetermined direction from the plane equivalent thereto. Theinclination direction is, for example, [1, 1, −2, 0] direction.

The polytype is not limited to 4H and it may be 6H or another one asneeded. Further, the crystal plane may be a plane other than the (0001)plane or the plane equivalent thereto.

Next, as shown in FIG. 7, an N− type SiC epitaxy layer 1 e (impurityconcentration of, for example, about 1×10¹⁶/cm³) having, for example, athickness of about 10 micrometers (in the case where the breakdownvoltage is about 1000V), which is varied according to a breakdownvoltage, is formed on the side of a surface 1 a of an N+ type SiCsemiconductor wafer 1 s.

Next, ion implantation is performed from the side of the surface 1 a ofthe wafer 1 to introduce therein a P type gate region 4 (normal gateregion) having, for example, a depth of about 1 micrometer. This ionimplantation can be divided into two sections. The process of the firstsection is carried out to obtain a junction with a vertical side surfaceand preferred examples include ion implantation under the followingconditions: aluminum as an ion source, a vertical implantation angle,implantation in five stages, and an implantation dose of each stagewithin a range of from about 1×10¹³/cm² to 5×10¹⁴/cm². This means thatimplantation is performed in plural stages while changing theimplantation energy within an implantation energy range of from about100 KeV to 700 KeV so as to achieve respectively different implantationdepths. An implantation temperature (wafer temperature at the time ofion implantation) is normal temperature unless otherwise specified. Suchmultistage implantation is effective for obtaining the P type gateregion 4 having a vertical side wall and is effective for forming achannel region with a high aspect ratio.

Similarly, the process of the second section is carried out for reducingcontact resistance. Preferred examples of it include ion implantationunder the following conditions: aluminum as an ion source, a verticalimplantation angle, implantation in two stages, and ion dose of eachstage within a range of from about 1×10¹⁵/cm² (at an implantationtemperature of, for example, about 500° C.) This means that implantationis performed in plural stages while changing the implantation energywithin an implantation energy range of from about 20 KeV to 100 KeV soas to achieve respectively different implantation depths. Thermaltreatment after ion implantation may be performed after each of thestages, but in the example shown below, it is performed once aftercompletion of these stages.

Next, as shown in FIG. 8, ion implantation is performed from the side ofthe surface 1 a of the wafer 1 to introduce therein a P type floatingregion 5 (floating gate region) having, for example, a depth of about 1micrometer. Preferred examples of this ion implantation process includethat under the following conditions: aluminum as an ion source, avertical implantation angle, implantation in two stages, and an ion doseof each stage within a range of from about 1×10¹²/cm² to 3×10¹³/cm².This means that implantation is performed in plural stages whilechanging the implantation energy within an implantation energy range offrom about 400 KeV to 700 KeV so as to achieve respectively differentimplantation depths. Thermal treatment after ion implantation may beperformed after each of the stages, but in the example shown here, it isperformed once after completion of these stages. Ion implantation may beperformed in a single stage, but multistage ion implantation isadvantageous from the standpoint of forming a vertical side surfaceunder control.

Next, as shown in FIG. 9, ion implantation is performed from the side ofthe surface 1 a of the wafer 1 to introduce therein a P type junctiontermination region 8 having, for example, a depth of about 1 micrometer(preferably in a range of, for example, from about 0.3 to 1.0micrometer). An ion dose is set so as to achieve complete depletion atthe time of maximum reverse bias. Preferred examples of this ionimplantation process include that under the following conditions:aluminum as an ion source, a vertical implantation angle, implantationin eight stages, and an ion dose of each stage within a range of fromabout 1×10¹¹/cm² to 5×10¹²/cm². This means that implantation isperformed in plural stages while changing the implantation energy withinan implantation energy range of from about 100 KeV to 700 KeV so as toachieve respectively different implantation depths. Thermal treatmentafter ion implantation may be performed after each of the stages, but inthe example shown below, it is performed once after completion of thesestages.

Next, as shown in FIG. 10, ion implantation is performed, for example,from the side of the surface 1 a of the wafer 1 to introduce therein,for example, a relatively shallow N+ type source region 6. Preferredexamples of this ion implantation process include ion implantation underthe following conditions: nitrogen as an ion source, a verticalimplantation angle, implantation in three stages, and a dose of eachstage within a range of from about 1×10¹⁵/cm² to 2×10¹⁵/cm². This meansthat implantation is performed in plural stages while changing theimplantation energy within an implantation energy range of from about 50KeV to 200 KeV so as to achieve respectively different implantationdepths. When the dose is from about 1×10¹⁵/cm² to 2×10¹⁵/cm², theimplantation temperature (wafer temperature during ion implantation) ispreferably set at, for example, about 700° C. (within a range of from300 to 800° C.) Then, activating thermal treatment is performed, forexample, for about one minute in an inert gas atmosphere (for example,at about 1700° C.)

Then, as shown in FIG. 11, a silicon oxide insulating film (for example,a TEOS-SiO₂ film) having a thickness of, for example, about 500 nm isformed on the surface 1 a of the wafer 1 as an interlayer insulatingfilm 17, for example, by CVD (chemical vapor deposition). Then, forexample, typical lithography is performed to process the interlayerinsulating film 17 into a source contact opening 21, a gate contactopening 22, and the like.

Then, as shown in FIG. 12, a silicide film such as nickel silicide filmis formed in, for example, the source contact opening 21 and the gatecontact opening 22 (together with formation of a silicide film on theback surface 1 b) to reduce contact resistance. Preferred examples ofthis silicidation annealing include that under the following conditions:in an argon atmosphere, at a temperature of about 1000° C., for aboutone or two minutes. Then, as shown in FIG. 12, a surface metal film 20is formed by sputtering film formation. Preferred examples of thesurface metal film 20 include a film comprised of, in order from thebottom, a titanium film (for example, about 50 nm thick), a titaniumnitride film (for example, about 50 nm thick), and an aluminum-basedmetal film (a metal film of about 500 nm thick having aluminum as a maincomponent)

Next, as shown in FIG. 13, a final passivation film 18 such as apolyimide film (for example, a photosensitive polyimide film) is formed,for example, by the method of application and then, the resulting filmis processed, for example, by typical lithography to form a source padopening 14 and the like.

Next, as shown in FIG. 14, a back-surface metal drain electrode 19 (forexample, titanium, nickel, gold, and the like from the side close to theback surface) is formed, for example, on the substantially whole surfaceof the back surface 1 b of the wafer 1, for example, by sputtering filmformation. Then, dicing or the like is performed to separate the waferinto individual chips 2.

4. Description on Modification Examples 1 to 4, in Unit Cell Structure(Source-island Type Cell Structure), of the Vertical-channel TypeJunction SiC Power FET (Vertical Planar Type Structure) According to theOne Embodiment of the Present Application (Mainly, from FIGS. 15 to 18)

This section describes various modification examples of the structurearound the channel region (the structure of the P type floating region 5and therearound) corresponding to FIG. 2 of Section 1. In this section,only portions not described above (mainly, those relating to FIG. 2)will be described in principle.

The following description will be specifically made mainly on theassumption that the device has a source-island structure (from FIG. 3 toFIG. 6). It is needless to say that the example of FIG. 2 in Section 1and each example in this section can be applied to each gate-islandstructure (Section 5) substantially as they are. They can also beapplied to other examples of the source-island structure (Sub-sections(1) and (2) of Section 5) substantially as they are.

FIG. 15 is a schematic cross-sectional view of a unit cell and regionstherearound corresponding to FIG. 2 for describing Modification Example1 (deep floating gate type source-island system cell structure) relatingto the unit cell structure (source-island type cell structure) in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present application.FIG. 16 is a schematic cross-sectional view of a unit cell correspondingto FIG. 2 and regions therearound for describing Modification Example 2(trapezoidal floating gate type source-island system cell structure)relating to the unit cell structure (source-island type cell structure)in the vertical-channel type junction SiC power FET (vertical planartype structure) according to the one embodiment of the presentapplication. FIG. 17 is a schematic cross-sectional view of a unit cellcorresponding to FIG. 2 and regions therearound for describingModification Example 3 (inverted T-shaped floating gate typesource-island system cell structure) relating to the unit cell structure(source-island type cell structure) in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application. FIG. 18 is a schematiccross-sectional view of a unit cell corresponding to FIG. 2 and regionstherearound for describing Modification Example 4 (two-stage epitaxyinverted T-shaped floating gate type source-island system cellstructure) relating to the unit cell structure (source-island type cellstructure) in the vertical-channel type junction SiC power FET (verticalplanar type structure) according to the one embodiment of the presentapplication. Based on these drawings, Modification Examples 1 to 4, inunit cell structure (source-island cell type structure), of thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present applicationwill be described.

(1) Deep Floating Gate Type Source-island System Cell Structure (Mainly,FIG. 15)

An additional characteristic of this example is that as shown in FIG.15, the lower end of the P type floating region 5 (floating gate region)extends below the lower end 4 b of the P type gate region 4 (normal gateregion). Even if there appears a difference in height between the lowerend of the P type floating region 5 (floating gate region) and the lowerend 4 b of the P type gate region 4 (normal gate region) due to processvariations, a sufficiently effective channel length can be secured. Onthe other hand, the example of FIG. 2 has the advantage that the ionimplantation step of the P type floating region 5 can be performedeasily at relatively low energies.

(2) Trapezoidal Floating Gate Type Source-island System Cell Structure(Mainly, FIG. 16)

An additional characteristic of this example is that as shown in FIG.16, the width of the lower end of the P type floating region 5 (floatinggate region) is wider than that of the upper end and this floatingregion has a trapezoidal cross-section. Such a shape makes it possibleto obtain an effect analogous to that of a lateral channel type. The ionimplantation step of this P type floating region 5 becomes a little morecomplex. Described specifically, this trapezoidal floating region isobtained, for example, by performing multistage ion implantation whilesetting the width of the opening of an ion implantation mask wider in alower stage or while using masks of the same width and implanting at avertical implantation angle in an upper stage and at an inclined anglein a lower stage.

(3) Inverted T-shaped Floating Gate Type Source-island System CellStructure (Mainly, FIG. 17):

In this example, as shown in FIG. 17, the P type floating region 5(floating gate region) of FIG. 15 is divided into two portions, that is,an upper P type floating region 5 t and a lower P type floating region 5b. In other words, the P type floating region 5 of FIG. 15 (the upper Ptype floating region 5 t in FIG. 17) has, at the lower end thereof, thelower P type floating region 5 b. When such a structure is employed, thechannel portion has at the lower end thereof a lateral channel so thatan advantage similar to that of a lateral channel can be obtained as asecondary advantage. On the other hand, this example has thedisadvantage that ion implantation at high energies is necessary for theformation of the lower P type floating region 5 b.

(4) Two-stage Epitaxy Inverted T-shaped Floating Gate Type Source-islandSystem Cell Structure (Mainly, FIG. 18)

In order to avoid the disadvantage of the example shown in FIG. 17, thisexample is formed, as shown in FIG. 18, by forming an N− type SiC lowerepitaxy layer 1ef, introducing therein a lower P type floating region 5b by ion implantation or the like, forming an N− type SiC upper epitaxylayer les, and then forming an upper P type floating region 5 t (the Ptype floating region of FIG. 15) in a manner similar to that of theexample of FIG. 15.

By forming the floating region as described above, a structure similarto that of FIG. 17 can be obtained without ion implantation atrelatively high energies. On the other hand, this epitaxial process hasthe advantage that it is performed in two stages.

5. Description on Modification Examples 1 and 2 (Source-island Type CellStructure) and Modification Examples 3 to 5 (Gate-island Type CellStructure), in Overall Layout of a Chip, of the Vertical-channel TypeJunction SiC Power FET (Vertical Planar Type Structure) According to theone Embodiment of the Present Application (Mainly, FIGS. 19 to 34)

This section describes modification examples mainly in a planar layout(layout of the active cell region 9 and regions therearound) describedin Section 2 referring to FIGS. 3 to 6. Only points not described abovewill hereinafter be described in principle.

Examples of Sub-sections (1) and (2) belong to, similar to the examplesof FIGS. 3 to 6, a source-island type cell structure, while examples ofSub-sections (3), (4), and (5) belong to a gate-island type cellstructure. The source-island type cell structure has the advantage thateven in a single-layer metal structure, it facilitates arrangement of awide source electrode at the center. The gate-island type cellstructure, on the other hand, has the advantage that leading of a gateand leading of a source can be made in a substantially symmetrical form.

The B-C cross-section in Sub-sections (1) and (2) are fundamentallysimilar to that described in FIG. 6, while the B-C cross-section inSub-sections (3) to (5) are fundamentally similar to that described inFIG. 28. In each example, an overlapping description is omitted inprinciple.

FIG. 19 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 3 for describing ModificationExample 1 (stripe type source-island system cell structure) relating tothe overall chip layout in the vertical-channel type junction SiC powerFET (vertical planar type structure) according to the one embodiment ofthe present application. FIG. 20 is an overall top view (having anemphasized contact portion while removing the upper surface metalstructure) of a chip corresponding to FIG. 19. FIG. 21 is an overall topview (having an emphasized impurity region while removing the uppersurface metal structure) of a chip corresponding to FIG. 19. FIG. 22 isan overall top view (including an upper surface metal structure) of achip corresponding to FIG. 4 for describing Modification Example 2(oblique lattice type source-island system cell structure) relating tothe overall chip layout in the vertical-channel type junction SiC powerFET (vertical planar type structure) according to the one embodiment ofthe present application. FIG. 23 is an overall top view (having anemphasized contact portion while removing the upper surface metalstructure) of a chip corresponding to FIG. 22. FIG. 24 is an overall topview (having an emphasized impurity region while removing the uppersurface metal structure) of a chip corresponding to FIG. 22. FIG. 25 isan overall top view (including an upper surface metal structure) of achip corresponding to FIG. 3 for describing Modification Example 3(square lattice type gate-island system cell structure) relating to theoverall chip layout in the vertical-channel type junction SiC power FET(vertical planar type structure) according to the one embodiment of thepresent application. FIG. 26 is an overall top view (having anemphasized contact portion while removing the upper surface metalstructure) of a chip corresponding to FIG. 25. FIG. 27 is an overall topview (having an emphasized impurity region while removing the uppersurface metal structure) of a chip corresponding to FIG. 25. FIG. 28 isa device cross-sectional view corresponding to the B-C cross-section ofFIG. 25. FIG. 29 is an overall top view (including an upper surfacemetal structure) of a chip corresponding to FIG. 3 for describingModification Example 4 (stripe type gate-island system cell structure)relating to the overall chip layout in the vertical-channel typejunction SiC power FET (vertical planar type structure) according to theone embodiment of the present application. FIG. 30 is an overall topview (having an emphasized contact portion while removing the uppersurface metal structure) of a chip corresponding to FIG. 29. FIG. 31 isan overall top view (having an emphasized impurity region while removingthe upper surface metal structure) of a chip corresponding to FIG. 29.FIG. 32 is an overall top view (including an upper surface metalstructure) of a chip corresponding to FIG. 3 for describing ModificationExample 5 (deformed oblique lattice type gate-island system cellstructure) relating to the overall chip layout in the vertical-channeltype junction SiC power FET (vertical planar type structure) accordingto the one embodiment of the present application. FIG. 33 is an overalltop view (having an emphasized contact portion while removing the uppersurface metal structure) of a chip corresponding to FIG. 32. FIG. 34 isan overall top view (having an emphasized impurity region while removingthe upper surface metal structure) of a chip corresponding to FIG. 32.Based on these drawings, Modification Examples 1 and 2 (source-islandtype cell structure) and Modification Examples 3 to 5 (gate-island typecell structure) relating to the overall chip layout in thevertical-channel type junction SiC power FET (vertical planar typestructure) according to the one embodiment of the present applicationwill next be described.

(1) Stripe-type (Modification Example 1) Source-island System CellLayout (Mainly, from FIG. 19 to FIG. 21)

As is apparent from FIG. 19 to FIG. 21, this example is basicallysimilar to that of from FIG. 3 to FIG. 6 and is characterized in thatthe unit cell region 10 runs longitudinally through the active cellregion 9. In this example, therefore, the P type gate regions 4 (normalgate regions) are arranged in a substantially stripe form in the activecell region 9 and they are linked with each other at the end portion ofthe active cell region 9. The lead-out of the gate can therefore becomprised of the metal gate wiring 16 provided around the active cellregion 9. The metal source electrode 15 can therefore be laid out widelyat the center portion.

(2) Oblique Lattice Type (Modification Example 2) Source-island SystemUnit Cell Layout (Mainly from FIG. 22 to FIG. 24)

As is apparent from FIG. 22 to FIG. 25, this example is basicallysimilar to that of from FIG. 3 to FIG. 6 and it is characterized in thatwhen two columns adjacent to each other are compared, their unit cellregions 10 are displaced obliquely to form an oblique lattice. Theplanar distribution of the channel regions can therefore be maderelatively uniform. Similar to the above example, the lead-out of thegate can therefore be comprised of the metal gate wiring 16 providedaround the active cell region 9. The metal source electrode 15 cantherefore be laid out widely at the center portion.

(3) Square Lattice Type (Modification Example 3) Gate-island System UnitCell Layout (Mainly from FIG. 25 to FIG. 28)

In the source-island structure (from FIG. 3 to FIG. 5), the N+ sourceregions 6 are arranged at the lattice points on the island in the activecell region 9. In this example, on the other hand, as is apparent fromFIG. 25 to FIG. 28, the P type gate regions 4 (normal gate regions) arearranged at the lattice points of the square lattice or orthogonallattice. In this example, therefore, in a single layer metal structure,the gate regions 4 are each led outside the active cell region 9 by acomb-shaped metal gate wiring 16.

In this layout, contrary to the source-island structure, the P typefloating regions 5 (floating gate regions) are in a mesh form in aplanar view (FIG. 27).

Further, this structure enables relative increase in the effectivechannel width.

Next, the B-C cross-section of from FIG. 25 to FIG. 27 is shown in FIG.28 (corresponding to FIG. 6). As is apparent from FIG. 6, asemiconductor substrate 2 has, in the surface region on the side of aback surface 1 b (second main surface) thereof, an N+ type drain region7 having, for example, a uniform thickness. The semiconductor substrate2 has, on a back surface 1 b thereof, a back-surface metal electrodefilm 19 (metal drain electrode film).

On the other hand, the semiconductor substrate 2 has, from the surfaceto the inside thereof on the side of the surface 1 a (first mainsurface), has, in this example, an N-type drift region 3 (for example,N− type SiC epitaxy layer 1 e) having a substantially uniform thickness.

The N− type drift region 3 (drift region) has, in the surface thereof,an N+ type source region 6 (source region) more heavily doped than thatof the N− type drift region 3. This N− type drift region 3 has therein aP type floating region 5 (floating region or floating gate region) so asto be below and close to the N+ type source region 6.

From the surface to the inside of the N− type drift region 3, a P typegate region 4 is provided so as to sandwich therewith the floatingregion 5 and the source region 4 at least from both sides thereof.Further, the P type gate region 4 at an end portion of the active cellregion 9 has, outside thereof, a P type junction termination region 8.

The semiconductor substrate 2 has, on the surface 1 a thereof, forexample, an interlayer insulating film 17 such as silicon oxide film.This interlayer insulating film 17 has thereon a metal source electrode15 and is electrically coupled to the N+ type source region 6 via asource contact portion 11. On the other hand, the interlayer insulatingfilm 17 has thereon a metal gate wiring 16 (metal gate electrode) and iselectrically coupled to the P type gate region 4 (normal gate region)via a gate contact portion 12. The interlayer insulating film 17, themetal source electrode 15, the metal gate wiring 16, and the like are,except for a portion thereof, covered with a final passivation film 18.

(4) Stripe-type (Modification Example 4) Gate-island System Unit CellLayout (Mainly, from FIG. 29 to FIG. 31)

This example employs a gate-island system corresponding to the stripetype source-island structure (from FIG. 19 to FIG. 21) and as isapparent from FIG. 29 to FIG. 31, it is characterized in that the unitcell region 10 runs longitudinally through the active cell region 9.Similar to the example of Sub-section (1), the structure in this examplehas the advantage of a simple cell structure.

In this example, on the other hand, the P type gate regions 4 (normalgate regions) are arranged in a substantially stripe form in the activecell region 9, but they are not linked with each other at the endportion of the active cell region 9. On the contrary, the P typefloating regions 5 (floating gate regions) are arranged in asubstantially stripe form in the active cell region 9 and they arelinked with each other at the end portion of the active cell region 9.

This example has also a characteristic of the gate-island system and ina single metal structure, the gate regions 4 are each led outside of theactive cell region 9 through the comb-like metal gate wiring 16.

(5) Deformed Oblique Lattice Form (Modification Example 5) Gate-islandSystem Unit Cell Layout (Mainly from FIG. 32 to FIG. 34)

This example employs a gate-island system corresponding to the obliquelattice type source-island structure (from FIG. 22 to FIG. 24) and as isapparent from FIG. 32 to FIG. 34, it is characterized in that unit cellregions 10 in the columns adjacent to each other are displaced obliquelyto form an oblique lattice. The P type floating regions 5 (floating gateregions) are, on the other hand, arranged in a stripe form in a planarview. This structure has the advantage similar to that of the example ofSub-section (1).

This example has also a characteristic of the gate-island system and ina single metal structure, the gate regions 4 are each led outside theactive cell region 9 through the comb-like metal gate wiring 16.

6. Complementary Description of the Above-mentioned Embodiment(Including Modification Examples) and General Consideration on theEmbodiment (Mainly, FIG. 35)

FIG. 35 is a fragmentary schematic cross-sectional view of a portioncorresponding to the unit cell of FIG. 2 for describing the outline ofthe vertical-channel type junction SiC power FET according to the oneembodiment of the present application. FIG. 36 is a circuit diagram of anormally off composite type transistor showing one example of a usingstate of the vertical-channel type junction SiC power FET according tothe one embodiment of the present application. Based on these drawings,the complementary description of the embodiment (including modificationexamples) and general consideration thereon will be carried out.

(1) Complementary Description of a Technical Problem and the Like:

As described above, in a SiC-based JFET (junction FET) showing amarkedly low impurity diffusion rate compared with a silicon JFET or thelike, a gate region is typically formed by forming a trench in a gateformation region and then carrying out ion implantation into the sidewall of the trench or the like. In order to secure the performance ofJFET, it is necessary to secure a gate depth while controlling adistance between gate regions with high precision. In other words, achannel region defined by the gate distance and the gate depth should beset at a high aspect ratio. Since a gate region is formed in a sourceregion because of the limitation of the process, a highly doped PNjunction is formed between the source region and the gate region, whichinevitably causes various problems such as increase in junction current.In addition, ion implantation at markedly high energies (about 2 MeV) isnecessary for manufacturing a termination structure (P type junctiontermination region).

As a method of forming a gate region without a troublesome trenchformation process, ion implantation at high energies can be given as acandidate. In this case, the distance between gate regions can becontrolled only by photolithography providing high precision and inaddition, the source region and the gate region can be separatedproperly by mask layout. This method is however not a complete technicalsolution because implantation at high energies is inevitable.

(2) Description on the Outline of the Vertical-channel Type Junction SiCPower FET According to the One Embodiment of the Present Application(Mainly, FIG. 35)

With a view to overcoming the above-described problem, according to theembodiment of the present application, as shown in FIG. 35, in thevertical-channel type junction SiC vertical FET, the floating gateregion 5 as well as as the normal gate region 4 having a gate potentialis provided below and contiguous to the source region 6 provided in thesurface region of the first main surface.

Such a structure enables formation of a high-aspect-ratio channelregion.

When the potential of the main gate region 4 is equal to the potentialof the source region 6, this structure (supposing that it has a normallyon mode) is ON-state. Application of a minus voltage to the main gateregion 4 extends a depletion layer to the side of the drift region 3 andlimits the flow of an electric current. At this time, the auxiliary gateregion 5 acts as a current limiting region. In other words, theauxiliary gate region 5 serves to decrease the thickness of the channeland thereby assists current control by the main gate region 4.

(3) Complementary Description of One Example of the Using State of theVertical-channel Type Junction SiC Power FET According to the Embodimentof the Present Application (Mainly, FIG. 36)

As the vertical-channel type junction SiC power FET (power JFET)according to the one embodiment of the present application, thatoperating in a normally on mode is shown specifically, because comparedwith a device operating in a normally off mode, the normally on modedevice has advantages such as manufacturing ease and superior switchingcharacteristics. Even if a normally on mode JFET is employed, it can beused as a cascode composite transistor HT as follows. As shown in FIG.36, a high breakdown voltage normally on mode JFET (Q1) as a main deviceand, for example, a low breakdown voltage silicon-based or SiC-basednormally off MOSFET (Q2) as an auxiliary device are cascade connected toeach other. This device can be regarded totally as a normally off modedevice having a drain terminal DJ of the normally on mode JFET (Q1), asource terminal SJ of the normally off MOSFET (Q2), and a gate terminalGM of the normally off MOSFET (Q2).

The auxiliary device Q2 may be either a silicon-based or a SiC-based oneinsofar as it is a normally off mode device. It may also be a MOS typeor a junction type device. Using a SiC-based one as the auxiliary deviceQ2 has the advantage that it permits operation at high temperatures of200° C. or greater. Using a silicon-based MOS device as the auxiliarydevice Q2, on the other hand, has the advantage that it enables costreduction and provides good switching characteristics.

7. Summary

The invention made by the present inventors has been describedspecifically based on the embodiment. The present invention is howevernot limited to it but needless to say, it can be changed in various wayswithout departing from the scope of the invention.

For example, in the above embodiment, mainly an N channel type powerJFET is specifically described. The invention is however not limited toit and needless to say, it can also be applied to a P channel type powerJFET. In the above embodiment, mainly a normally on type power JFET isspecifically described. The invention is however not limited to it andneedless to say, it can also be applied to a normally off type powerJFET.

In the above embodiment, an active device (such as FET, IGBT, or diode)using mainly a silicon carbide (SiC)-based semiconductor substrate (notonly a 4H polytype but also a 6H polytype or the like) is describedspecifically. The invention is not limited to it and needless to say, itcan also be applied to a GaN-based active device or the like.

In the above embodiment, a junction termination structure is describedspecifically with a junction termination extension as an example. Thejunction termination structure is however not limited to it and needlessto say, it may be, for example, a field limiting ring, a field plate, acomposite structure of them, or the like structure.

What is claimed is:
 1. A vertical-channel type junction SiC power FET,comprising: (a) a SiC semiconductor substrate having a first mainsurface and a second main surface; (b) a drift region provided from asurface of the first main surface toward the second main surface of theSiC semiconductor substrate and having a first conductivity type; (c) adrain region provided in a surface region of the second main surface ofthe SiC semiconductor substrate, more heavily doped than the driftregion, and having the first conductivity type; (d) an active cellregion extending from a surface of the first main surface to an insideof the drift region; and (e) a plurality of unit cell regions providedin the active cell region, wherein each of the unit cell regionscomprises: (e1) a source region provided in a surface region of thedrift region, more heavily doped than the drift region, and having thefirst conductivity type; (e2) a floating region provided in the driftregion so as to be below the source region and having a secondconductivity type, that is, a conductivity type opposite to the firstconductivity type; and (e3) gate regions provided in a surface region ofthe drift region so as to sandwich therewith the source region and thefloating region at least from two sides thereof and having the secondconductivity type, wherein the floating region extends, in a depthdirection thereof, at least from a region between the gate regions to alower end of the gate regions.
 2. The vertical-channel type junction SiCpower FET according to claim 1, wherein a device structure is a planartype.
 3. The vertical-channel type junction SiC power FET according toclaim 1, wherein an operation mode is a normally-on type.
 4. Thevertical-channel type junction SiC power FET according to claim 1,wherein the floating region is formed by ion implantation.
 5. Thevertical-channel type junction SiC power FET according to claim 1,wherein the gate regions are formed by ion implantation.
 6. Thevertical-channel type junction SiC power FET according to claim 1,wherein the floating region is within the width of the source region ina planar view.
 7. The vertical-channel type junction SiC power FETaccording to claim 1, wherein the gate regions are arranged in a stripeform in in a planar view.
 8. The vertical-channel type junction SiCpower FET according to claim 7, wherein the gate regions are linked witheach other at an end portion of the active cell region in a planar view.9. The vertical-channel type junction SiC power FET according to claim1, wherein the floating region is formed by multistage ion implantation.10. The vertical-channel type junction SiC power FET according to claim1, wherein the gate regions are arranged in a mesh form in a planarview.
 11. A vertical-channel type junction SiC power FET, comprising:(a) a SiC semiconductor substrate having a first main surface and asecond main surface; (b) a drift region provided from a surface of thefirst main surface toward the second main surface of the SiCsemiconductor substrate and having a first conductivity type; (c) adrain region provided in a surface region of the second main surface ofthe SiC semiconductor substrate, more heavily doped than the driftregion, and having the first conductivity type; (d) an active cellregion extending from a surface of the first main surface to an insideof the drift region; and (e) a plurality of unit cell regions providedin the active cell region, wherein each of the unit cell regionscomprises: (e1) a source region provided in a surface region of thedrift region, more heavily doped than the drift region, and having thefirst conductivity type; (e2) a floating region provided in the driftregion so as to be below the source region and having a secondconductivity type, that is, a conductivity type opposite to the firstconductivity type; and (e3) gate regions provided in a surface region ofthe drift region so as to sandwich therewith the source region and thefloating region at least from two sides thereof and having the secondconductivity type, wherein the gate regions are arranged in a mesh formin a planar view.
 12. A method of manufacturing a vertical-channel typejunction SiC power FET, comprising the steps of: (a) providing an SiCsemiconductor wafer having a first main surface and a second mainsurface, a drift region extending from a surface of the first mainsurface toward the second main surface of the SiC semiconductor waferand having a first conductivity type, and a drain region provided in asurface region of the second main surface, more heavily doped than thedrift region, and having the first conductivity type; and (b)introducing, from a surface of the first main surface to an inside ofthe drift region, an active cell region having a plurality of unit cellregions, wherein the step of introducing the active cell region isperformed for each of the unit cell regions and comprises the sub-stepsof: (b1) introducing, in a surface region of the drift region, a sourceregion more heavily doped than the drift region and having the firstconductivity type; (b2) introducing a floating region having a secondconductivity type, which is a conductivity type opposite to the firstconductivity type, in the drift region so as to be below the sourceregion; and (b3) introducing gate regions having the second conductivitytype in a surface region of the drift region so as to sandwich therewiththe source region and the floating region at least from two sidesthereof, wherein the floating region extends, in a depth direction, atleast from a region between the gate regions to a lower end of the gateregions.
 13. The method of manufacturing a vertical-channel typejunction SiC power FET according to claim 12, wherein the floatingregion is introduced by ion implantation.
 14. The method ofmanufacturing a vertical-channel type junction SiC power FET accordingto claim 13, wherein the floating region is introduced by multistage ionimplantation.
 15. The method of manufacturing a vertical-channel typejunction SiC power FET according to claim 12, wherein the gate regionsare introduced by ion implantation.
 16. The method of manufacturing avertical-channel type junction SiC power FET according to claim 12,wherein a device structure is a planar type.
 17. The method ofmanufacturing a vertical-channel type junction SiC power FET accordingto claim 12, wherein the sub-step (b2) is performed after the sub-step(b3).
 18. The method of manufacturing a vertical-channel type junctionSiC power FET according to claim 12, wherein the sub-step (b2) isperformed before the sub-step (b1).
 19. The method of manufacturing avertical-channel type junction SiC power FET according to claim 12,wherein the floating region is within the width of the source region ina planar view.